484 AN INTRODUCTION TO ENTOMOLOGY 



Family GYRINID.E 



The Whirligig-Beetles 



As familiar to the country rover as the gurgling of the brook or 

 the flecks of foam on its "golden -braided centre," or the trailing ferns 

 and the rustling rushes on its banks, are these whirligigs on its 

 pools. Around and around each other they dart, tracing graceful 

 curves on the water, which vanish almost as soon as made. They 

 are social fellows, and are almost always found in large numbers, 

 either swimming or resting motionless near together. They rarely 

 dive, except when pursued; but are so agile that it is extremely 

 difficult to catch them without a net. Many of them when caught 

 exhale a milky fluid having a very disagreeable odor. They feed 

 upon small flies, beetles, and other insects that fall into the water, 

 and are furnished with well-developed wings, with which they fly 

 from one body of water to another. 



This is one of the most easily-recognized families of the whole 

 order Coleoptera. The members of it are oval or elliptical in form 

 (Fig. 570), more or less flattened, and usually of a very 

 brilliant bluish black color above, with a bronze metallic 

 lustre. The fore legs are very long and rather slender; the 

 middle and hind legs are short, broad, and very much 

 flattened. These insects are remarkable for having the eyes 

 completely divided by the margin of the head, so that they 

 appear to have four eyes — a pair upon the upper surface of 

 the head with which to look into the air, and a pair upon 

 the under side for looking into the water. The antennae are very short 

 and peculiar in form. The third segment is enlarged, so as to resemble 

 an ear-like appendage, and the following ones form a short spindle- 

 shaped mass. They are inserted in little cavities in front of the eyes. 



The eggs of these insects are small, of cylindrical 

 form, and are placed end to end in parallel rows upon 

 the leaves of aquatic plants. The larvae (Fig. 571) 

 are long, narrow, and much flattened. Each abdominal 

 segment is furnished with a pair of tracheal gills, and 

 there is an additional pair at the caudal end of the 

 body. The elongated form of the body and the con- 

 spicuous tracheal gills cause these larvse to resemble 

 small centipedes. When a larva is full-grown it leaves 

 the water and spins a gray, paper-like cocoon attached 

 to some object near the water. The pupa state of those 

 species in which it has been observed lasts about a 

 month. Fig. 571. 



The family is a small one. At present only forty-one 

 North American species are known. These represent three genera. 

 The genus Gyretes is distinguished by having the last ventral segment 

 of the abdomen elongated and conical. It is represented by two 

 species. In the other two genera the last ventral segment is flattened 

 and rounded at the tip. In DineUtus the scutellum is invisible ; there 

 are thirteen species of this genus. In Gyrlnus the scutellum is visible; 

 of this genus we have twenty-six species. 



